One of the most promising technologies in the capture and storage of carbon dioxide (CO2) is related to the fixation of this gas in the form of insoluble inorganic carbonates. This fixation is achieved by a chemical reaction, known as mineral carbonation or mineral sequestration. The use of calcium-rich minerals from industrial waste or urban solid waste, Journal of Hazardous Materials B128, 73-79 (2006), is one strategy proposed for increasing technological and economic viability of mineral sequestration of CO2. For example, techniques for reusing residues rich in calcium hydroxide from the paper industry (Journal of Hazardous Materials 161, 1347-1354 (2009)) or the acetylene production industry (Chemical Engineering Journal 166, 132-137 (2011)) have been proposed. These lines of work have been studied at a theoretical level. Lackner et al., (2nd U.S.-China Symposium on CO2 Emissions Control Science & Technology May 28-30, 2008) for example compared renewable energy technologies (aerogenerators and photovoltaic plates) to a combined technology of energy generation plants based on fossil fuels together with CO2 sinks. The main problem with this mineral sequestration technique for CO2 is the large amount of calcite generated as a result of the currently enormous CO2 emissions.
Other authors in basic research studies have proposed the use of lime from mineral calcite for separating mixtures of industrial gases (U.S. Pat. No. 7,618,606B2). Strategies have been developed for temporary capture of CO2 by mineral fixation and its regeneration by cycles of calcination and carbonation (Energy Fuel 2006; 21:163-70), considering methods for regenerating and reactivating the sorbent, lime (Chemical Engineering Journal 2010; Volume 156, Issue 2, Pages 388-394). These routes have been proposed for separating CO2 from a mixture of gases for its geological sequestration (Progress in Energy and Combustion Science 2010; Volume 36, Issue 2, Pages 260-279).
The technology and current process for reducing SO2 emissions in combustion gas currents is based on contact between the gas and an aqueous suspension of mineral calcite. This aqueous suspension is obtained by crushing the calcite obtained from mines and subsequent addition of water to create a calcite slurry. This process requires mining activities, with the consequent harm to the landscape, CO2 emissions due to huge energy consumption during extraction (5-11 kg CO2 per hour), crushing (174-412 kg CO2 per hour) and transport of the mineral (50-118 kg CO2 per hour); currently there are studies seeking cycles of calcination and carbonation to reactivate the calcite in the process of capturing SO2 (Energy Fuel 2008; Volume 87, Issue 13-14, Pages 2923-2931); there are also patents where the mineral calcite is prepared with certain physical properties, large surface area and high pore density that make it more reactive toward SO2 (U.S. Pat. No. 5,779,464 (A)).
In one of the option currently used, this slurry is led to a damp scrubber (EP1958682A1 and JP61167432A) where it is pumped from the bottom of the scrubber to sprayers at the top. There it atomises and comes into contact with a countercurrent of SO2, which is absorbed in the form of CaSO3. The calcium sulphite falls to the bottom of the scrubber where bubbling air oxidises the CaSO3 to CaSO4 for removal from the process (Fuel 1995; Volume 74, Issue 7, Pages 1018-1023).
Another option that is currently used is a semi-dry scrubber. The difference between this and the wet scrubber is based on the pumping of the slurry, which is performed with just the right amount of water so that it is completely evaporated by spraying. The absorption of SO2 takes place while the slurry evaporates, thus producing the dry product, CaSO4.
These two options have the drawback that, on only capturing the SO2, the used calcite generates CO2 that is emitted to the atmosphere.
The removal of SO2 from the gases by scrubbers has given rise to new studies and/or patents seeking ways of regenerating the sorbent that captures the SO2. This regeneration is mainly based on adding a reagent to the products generated in the capture of the SO2 to obtain the initial sorbent and other secondary products. Thus, JP2000051649A reveals the use of Mg(OH)2 for capturing SO2. Subsequently a calcium salt is added in caustic soda to regenerate Mg(OH)2 and also to form gypsum and a sodium salt. Another process proposed in U.S. Pat. No. 7,247,284B1 is based on the capture of SO2 with caustic soda, followed by subsequent addition of Ca(OH)2 to the Na2SO4 formed, thereby regenerating the caustic soda and precipitating the gypsum.
These processes are applied only to the reduction of SO2 emissions, this being their main negative aspect, as well as the generation of large amount of gypsum and other products such as sodium salts (Fuel 1995; Volume 74, Issue 7, Pages 1018-1023), which affect the aquatic environment as they are in the form of brine. Envirotech Corporation (U.S. Pat. No. 3,873,532 (A)) proposed the prior absorption of SO2 with a caustic soda solution, subsequently adding lime to regenerate the original soda.
For the combined reduction of CO2 and SO2, U.S. Pat. No. 5,958,353A proposed the absorption of CO2 and/or SO2 with a basic solution, subsequently adding a soluble calcium salt and so fixing the CO2 and/or SO2 as CaCO3 and CaSO3 respectively and together, using commercial pure sorbents at all times.
Therefore it is necessary to develop a process for capturing CO2 and SO2 that avoids the problems described above.